This is OK as far as I know. I've done this to test Ovalplus lights in the past. Be aware the capacitor that powers the LED will likely sap a little bit out of the battery capacity (but not much, I imagine).

If it had been an E6 then definitely no... the power surge plays absolute havoc with the magnetic reed switch. The Ovalplus switch, if it has one, is straightforward electrical switch.

I have wired a Basta 6V/2,4W generator light like this and used it for several months now. I'm using rechargeable AAs with 1,2V nominal voltage, so I have 6 of them. The battery package delivers more than the recommended +20% overvolting when freshly charged, but so far the bulb has taken it OK. The Oval Plus standlight feature shouldn't be a huge issue.